The present invention relates to a system for recording and/or reproducing a pulse code modulation (PCM) digital audio signal, and more particularly, to a system for recording and/or reproducing a PCM digital audio signal, in which digital audio signals can be recorded on a digital recording medium or can be reproduced from the digital recording medium, even though sampling frequencies of the PCM digital audio signals differ from each other.
All apparatuses which use PCM digital audio signals use a reference unit, which is a data unit for enabling error correction. The size of the reference unit is determined according to the features of a transmission medium. A digital audio signal which has been sampled according to a predetermined sampling frequency is recorded on a recording medium in the form of blocks having a size, or amount of data, which is determined according to a data recording characteristic of the recording medium, such as a compact disk (CD), a digital audio tape (DAT) and so on. When a reproduction operation is performed with respect to the recording medium, a digital-to-analog converter converts a digital audio signal into an analog audio signal in the sequence of the outflow of the data from the recording medium.
As to PCM digital audio signals, in order to replace an existing system which uses sampling frequencies of 44.1 KHz or 48 KHz, with new audio recording systems which use sampling frequencies of 88.2 KHz or 96 KHz, for example, an advanced audio (ADA) system in Japan, has been proposed. However, the existing reproduction system which uses the sampling frequencies of 44.1 KHz or 48 KHz, cannot reproduce audio signals which have been recorded in a digital form according to the newly proposed system. Therefore, in order to allow such an existing reproducing system to reproduce a digital audio signal which has been recorded according to a new recording system, separate digital signal processing is required so that a bit number representing each sample without creating noise can be handled. Examples of the required digital signal processing include, low-pass filtering to eradicate a frequency component higher than 44.1 KHz or 48 KHz from a signal read from a recording medium, and decimation filtering to make the low-pass filtered signal into a signal having the sampling frequency of 44.1 KHz or 48 KHz.
For this reason, the existing reproduction system should process all input audio data in order to reproduce an audio signal according to the newly proposed system. Consequently, a digital processor having an operating frequency larger than a sampling frequency of the input audio data, is required. However, it is expensive to improve the existing reproducing system in order to reproduce a digital audio signal of the proposed signal recording system. Also, additional RAM capacity is required for the above-described separate digital signal processing, also increasing the cost necessary for such an improvement.
Meanwhile, a reproducing system which includes a digital-to-analog converter having sampling frequencies of 88.2 KHz or 96 KHz, directly transmits received data to an output terminal without processing the received data. Thus, a digital processor for processing audio data and a large amount of RAM capacity are not required. However, if another audio recording system using a frequency higher than 88.2 KHz (or 96 KHz) is proposed, the same problems as those of existing system will be created.